1. Field of the Invention
In general, the present invention is an apparatus, system, and method for sensing liquid level in a vessel. More in particular, the present invention generally provides a fully encapsulated liquid level sensor using optical properties for highly accurate monitoring the liquid level in a vessel.
2. Description of the Prior Art
Electrical optical sensing devices are well known in the field of liquid level sensors. They generally employ reflective and refractive optical theory based on the different indices of refraction between two media. Typically, these devices require the liquid to pass between two surfaces wherein the light change is measured as the liquid passes between two locations or through a space.
One such sensor is described in U.S. Pat. No. 4,711,126, which issued to Houpt et al. on Dec. 8, 1987. Houpt teaches a Y-shaped light probe having a single light source at one arm of the Y, and a single light detector at the other. The wall of the probe is coated with a reflective material with windows in the form of thin rings cut out in the reflective material. As the light travels from the light source to the bottom of the sensor, and reflects back to the detector, some of the light is lost through the windows to the outside liquid by refraction. The liquid level is determined by the amount of light that reflects and travels back to the detector.
Another optical liquid level sensor is described in U.S. Pat. No. 3,995,169, issued to Oddon on Nov. 30, 1976. This invention teaches a sensor consisting of a plurality of U-shaped light pipes of various length, each with a light source and a light detector at respective ends of the pipe. The geometry and construction of the pipe is such that the light reflects back to the detector end if liquid is not present at the U bend of the pipe, and refracts out of the pipe if liquid is present.
In U.S. Pat. No. 4,354,180 issued to Harding on Oct. 12, 1982, an electro-optical liquid level sensor is described. Harding teaches a sensor also of probe type configuration, using reflection or refraction of a light beam to determine the liquid level. This sensor detects only at a single level, usually for maximum level or minimum level indication, rather than multi-point liquid level monitoring capability of the present invention.
In U.S. Pat. No. 4,904,878 issued to Gipp, et al. on Feb. 27, 1990, another electro-optical liquid level sensor is described. Gipp, et al. also provides a sensor, which requires the liquid to pass between a first housing portion that is spaced from the second housing portion wherein liquid may pass through.
All these prior art devices have the disadvantage of requiring the light to bounce or be received across a space wherein the space must have the liquid pass through. This obviously creates a region that can be blocked by contaminants and impurities in the liquid thereby making the measurements inaccurate when the amount of light returning to the detector is not true to the level of liquid to be measured. Each of the above identified electrical optical liquid level sensors and others in the field are adequate in certain situations, but may create difficulties due to the nature of the device and the need for two surfaces, areas, and/or sensors for the liquid to pass.
In the U.S. Pat. No. 7,161,165 issued to Wirthlin on Jan. 9, 2007, an optical transducer for liquid level determination is described that does not require the liquid to pass through two points. Radiant energy from the light source is projected into a probe until it hits a reflective element, whereupon it is reflected back towards a photo sensor. The obvious disadvantage is the required addition of a reflective element and the cost accordingly to provide such configuration as well as the problems associated with using large vessels and the distance of reflections accordingly.
In view of the above, there is currently a need for a device that is more reliable, better construction and that eliminates the need for the liquid to pass between sensors. Currently in the prior art, there is no device or system which is sufficiently sensitive, inexpensive, and robust enough for common daily usage and especially in volatile environments or where extremely accurate readings are desired.
The above discussion is not to be considered exhaustive, however, does demonstrate that a need exists for a more accurate and reliable means to detect liquid levels in vessels. The industry is looking for solutions, methods, and systems to address these needs and there is an obvious need to fill the gap where the prior art has failed. What is needed is an apparatus, system and method to address these shortcomings in the prior art while also addressing the significance of the issues presented.